Various silicon-containing materials can be used as precursors to silicon dioxide. For example, silsesquioxane resins, silicate esters and hydrolyzed products thereof, polysilazanes, polycarbosilanes, and combinations thereof are known in the art.
Methods of forming silicon dioxide ceramic coatings are known in the art. For example, U.S. Pat. No. 5,336,532 issued to Haluska et al. on Aug. 9, 1994, and U.S. Pat. No. 5,318,857 to Haluska et al. on Jun. 7, 1994, disclose methods of forming silicon dioxide containing ceramics on microelectronic devices. The methods comprise forming a coating of a ceramic precursor on the device and heating the precursor to a temperature of 40 to 400.degree. C. in the presence of ozone. The ceramic precursor in U.S. Pat. No. 5,336,532 comprises hydrogen silsesquioxane resin. The ceramic precursor in U.S. Pat. No. 5,318,857 comprises a hydrolyzed or partially hydrolyzed silicon alkoxide.
U.S. Pat. No. 5,262,201 issued to Chandra et al. on Nov. 16, 1993, discloses a method of making ceramic coatings. The method comprises heating a ceramic precursor to 20 to 500.degree. C. in an atmosphere comprising aqueous ammonia or ammonium hydroxide.
Methods of forming ceramic-like coatings containing silicon dioxide are also known in the art. For example, U.S. Pat. No. 5,290,354 issued to Haluska on Mar. 1, 1994, discloses a method forming a ceramic or ceramic-like coating on a substrate, such as an electronic device, as well as the substrate coated thereby. The method comprises coating the substrate with a solution comprising a solvent, hydrogen silsesquioxane resin and a metal oxide precursor. The solvent is then evaporated, thereby depositing a pre-ceramic coating on the substrate. The pre-ceramic coating is then ceramified by heating to a temperature of 40.degree. C. and 1,000.degree. C. This coating may be covered by additional passivation and barrier coatings.
U.S. Pat. No. 5,145,723 issued to Ballance et al. on Sep. 8, 1992 discloses a method of forming a silica coating on a substrate. The method comprises coating a substrate with a silica precursor having a melting point between 50.degree. C. and 450.degree. C. The coating is heated to a temperature above its melting point in an inert environment to allow the coating to melt and flow. The melted coating is then heated in an environment which facilitates conversion to silica for a time sufficient to convert it to silica.
U.S. Pat. No. 5,399,441 issued to Bearinger, et al. on Mar. 21, 1995 discloses a method of forming opaque coatings on integrated circuits. The method comprises applying a coating of a silica precursor resin and a filler onto the integrated circuit and heating the coated circuit to a temperature of 50 to 1000.degree. C. to form a silica containing ceramic. The silica precursor resin can comprise hydrogensilsesquioxane resin and hydrolyzed or partially hydrolyzed alkoxysilanes, and may be heated in an oxidizing or non-oxidizing atmosphere.
U.S. Pat. No. 5,710,203 issued to Camilletti et al. on Jan. 20, 1998 discloses a method of forming a tamper-proof coating on an electronic device. The method comprises applying a coating of a silica precursor resin and a filler onto the electronic device, wherein the filler is one which reacts in an oxidizing atmosphere to liberate enough heat to damage the electronic device. The coated electronic device is then heated at a temperature sufficient to convert the silica precursor resin to a silica containing ceramic matrix.
U.S. Pat. No. 5,508,062 issued to Frye et al. on Apr. 16, 1996 discloses a method of forming an insoluble coating on a substrate. The method comprises mixing a composition comprising an alkoxysilane and a titanium catalyst to form a coating mixture. The coating mixture is then applied on a substrate and then exposed to atmospheric moisture for a time sufficient to form an insoluble coating. Finally, the substrate having the insoluble coating is heated at a temperature between 100 and 600.degree. C. for up to 6 hours.
U.S. Pat. No. 5,711,987 issued to Bearinger et al. on Jan. 27, 1998 discloses a method of forming a tamper-proof coating on an electronic device by (1) applying on the device a composition comprising pre-ceramic silicon-containing material and filler and thereafter ceramifying the pre-ceramic silicon-containing material and (2) applying over the ceramic layer a sealer layer produced from a colloidal inorganic-based siloxane resin, benzocyclobutene based resin, polyimide resin, siloxane polyimides and parylene and thereafter curing the resin. The coating may further comprise optional third (amorphous SiC:H, diamond, silicon nitride and parylene) and fourth layers (same as second layer).
However, none of these methods disclose polysilastyrene as a precursor to silicon dioxide.
Therefore, it is an object of this invention to provide a method of using polysilastyrene to form a silicon dioxide containing coating on a substrate, such as an electronic device.
It is a further object of this invention to provide a method of forming a multi-layer coating on a substrate, wherein at least one layer is a silicon dioxide containing coating made from a coating composition comprising polysilastyrene.